It is known that cellulosic esters containing alpha, beta unsaturation are useful as resins and modifying resins in formulating photocurable compositions for use, such as, protective coatings for wood and other solid substrates. For example, U.S. Pat. Nos. 4,565,857; 4,654,233; 4,656,202 and 3,749,592 describe photocurable coating compositions comprising polymerizable monofunctional ethylenically unsaturated cellulosic esters derived from the reaction of a hydroxyl functional cellulosic ester and a monoethylenically unsaturated compound having a hydroxyl reactive group, for instance, 2-isocyanatoethyl acrylate or methacrylate, or a monourethane.
Such photocurable compositions have certain drawbacks, however, in that toxic or irritating reactive diluents or plasticizers are needed to crosslink with the ethylenically unsaturated cellulosic esters to maximize solvent resistance and strength of the cured coating, which in turn, provide for additional handling and manufacturing problems. The present invention avoids such drawbacks by providing a novel photocurable coating composition with greatly improved crosslinking efficiency, and which significantly reduces or eliminates the need for reactive diluents or plasticizers and the like to provide maximum solvent resistance and strength in cured products manufactured therefrom. Accordingly, the present invention provides a photocurable coating composition comprising a polyfunctional cellulosic polymer having an average of at least 1.5 terminal alpha,beta-ethylenic unsaturations per substituted position of anhydroglucose unit of the polymer which is derived from the reaction product of (a) at least one cellulosic polymer having isocyanate reactive hydroxyl functionality, and (b) at least one hydroxyl reactive poly(alpha,beta-ethylenically unsaturated) isocyanate produced from the reaction of
(i) a hydroxyl functional (meth)acrylic ester with PA1 (ii) a polyisocyanate having an average of at least three hydroxyl reactive isocyanate groups.
The following detailed description is more fully illustrative of the present invention.